Guru Pūrṇimā is also called Vyāsa Pūrṇimā, because tradition holds that Vyāsa, who divided the Veda into four and composed the Mahābhārata and the Purāṇas, was born on this full moon. Every teacher in the tradition is seen as seated on the "seat of Vyāsa" (vyāsa-pīṭha), so honouring one's guru is honouring him.
For renunciants it begins Cāturmāsya, the four months of the rains spent in one place in study. Buddhists celebrate the same full moon as the day of the Buddha's first sermon at Sārnāth.
